I play a variety of music, some classical, some popular.

I acquired some old sheet music for a popular song that requires a fast left hand pulse underlying the right hand melody. Like "da-da-da-da-da-da---da-da-da-da-da-da." The left hand chords change with the measure but the pulse continues. It is rather rapid-- sixteenth notes, I believe. The piece is entitled "Love is All We Need" and was popular in the 1950s.

I prepared this on my grand at home, then went to my lesson and was required to play this on an upright at the studio. I believe the upright there was a Yamaha.

I had a great deal of difficulty with the piece at the teaching studio, and after playing most of the first page, just stopped. I told the teacher "this just isn't working."

The upright felt sort of spongy or "soggy," and it was very hard to get a crisp, clean pattern out of the left-hand pulse.

My teacher suspected the grand action just is more condusive to crisp delivery of this pattern. She said that this may be one of those infrequent situations where the particular line of music really reflects the different mechanics of grand vs. upright actions.

I continue to be able to play the piece on my grand at home, with good results. In fact, I just played it yesterday.

Does anyone have any comments?

Uprights are very sensitive to capstan adjustments. A lot of lost motion will make them play very poorly. It is not difficult nor expensive to adjust them, but few people get it done.

On vertical pianos you must let the key return nearly all the way up before the mechanism reset and be ready to play another note.
On grands all you need do is to release the pressure (about the thickness of two business cards) on the key and the mechanism resets and is ready to repeat.
It is amazing to me how many teachers and performers do not know this basic fact about their instrument.

On the other hand...

I never had a problem with repeating in the intermediate/advanced playing that I have done on uprights while studying.

I don't know...maybe it is just me, but the only piece that I remember needing a quick return/repeat was a Rhapsody in Blue section. Maybe I just adjusted to what I had to play on?

Craigen...you are absolutely right...not enough teachers mention this difference. But often their students might not need to know until they get into some specific pieces how to play fast repeats on their home instruments.

Edit- best add-

When repeating a single note fast, crisp staccato action is used - so pianists might let the key return as they adjust to an upright action?

In one year, I have yet had to adjust to a grand for quick repeats. Is this just me?