What follows here are the actual quotes from documents linked to his post.
TO THE LIMITS OF THE SOUL'S IDEAL: GETTYSBURG gives the following extract mentioning a V Corps source (problem - the footnote link sourcing the quote is broken):
At a turn of the road a staff officer, with an air of authority, told each colonel as he came riding up, that McClellan was in command again, and riding ahead of us on the road. Then wild cheers rolled from the crowding column into the brooding sky, and the earth shook under the quickened tread.This material is from Henry Hunt [my emphasis added]:
A suggestive incident is worth recording here. In the course of my inspection of the lines that morning, while passing along Culp's Hill, I found the men hard at work intrenching, and in such fine spirits as at once to attract attention. One of them finally dropped his work, and, approaching me, inquired if the reports just received were true. On asking what he referred to, he replied that twice word had been passed along the line that General McClellan had been assigned to the command of the army, and the second time it was added that he was on the way to the field and might soon be expected. He continued, "the boys are all jubilant over it, for they know that if he takes command everything will go all right." I have been told recently by the commander of a Fifth Corps battery, that during the forced march of the preceding night the same report ran through that corps, excited great enthusiasm amongst the men, and renewed their vigor. It was probably from this corps -- just arrived -- that the report had spread along the line.William Lochren of the 1st Minnesota writes:
On Saturday, June 28th, we passed Urbana, and halted on the Monocacy, in view of Frederick City. This beautiful valley seemed filled with troops, artillery and wagon trains. Here the news that Hooker had resigned and that Meade was in command, caused a momentary depression, soon changed to elation by a rumor that McClellan was to be restored to command, - a rumor that he was on his way to join us cheering us at Gettysburg a few days later.So there is a pre-Gettysburg rumor as well. The Fourth Maine heard it too:
On the 28th the 4th Maine arrived at Walkerville. Here the land was rich in crops and fences were still standing, not like the stripped land in Virginia. MG George G. Meade is appointed as commander of the Army of the Potomac. There was a rumor in the army that the appointment was only temporary and that MG McClellan would be given command of the army again. This helped to raise the men's spirits.Scott Hartwig blames General Alexander Webb for spreading a false rumor, but does not adequately endnote his surmise:
The evening before the fighting in this sector had caused consternation in the ranks of the 69th [Pennsylvania], for the men were unaware that the Union front hooked around to the east. Brigade commander Web, who was probably just as ignorant of the army's general dispositions attempted to allay the fears of his men by spreading the false rumor that Maj. General George B. McClellan would arrive in Gettysburg in the Confederate rear the following afternoon with 30,000 men. Either because of Webb's story-telling or knowledge that powerful Union forces had been moved to confront the Confederates on Culp's Hill, the morning struggle for the hill did not elicit the concern of the evening before within the ranks.
Fascinating stuff, and a look into unsanitized "history as experienced".