Not seen that with Lewisia.

Maybe then I plant deeper. Lewisia tend to last 3 to 5 years here, planted in a sunny location along a stone path (viz. dry location).

Below: 'Little Plum', a Lewisia longipetala x cotyledon hybrid.

So what exactly do you mean by "the stems are getting rather long, with foliage just at the top". Is there foliage comming out at the stem where the flowers should be? Or is the basal clump of foliage getting "tall" with a naked stem between the folaige and the ground?

IF it is the former (which I doubt- it's pretty rare) it could be a cell mutation- think its called proliferation.

If it is the latter I would think some die-off with the older, lower leaves would be typical. I wouldn't plant any deeper- I've always read they need their crowns above ground so they don't rot out. That being said I've only tried to grow Lewisia once and failed epically ;-)

You might always try asking this on the alpine forum btw...
CMK

Just pile a few rocks around it - that's what I do when they do that. They like rocks anyway, and the right rocks will really show them off.