Hmmm - while U. graminifolia can be tough for some to coax into flower mode, I hadn't heard that it was big on aborting stalks.... However, otoh, U. subulata produces cleistogamous flowers frequently..... very suspicious...I can't seem to get mine to flower. I have about a dozen of flower stalks with little buds, but they never bloom. I'll get some picks up soon.
Keep it watered down real good and it should take right off.
I grow mine in a little 2.5 gallon tank in flourite. I keep the water level with the flourite.
How deep is your medium? I got a small plug from Jimscott several years ago and I put it in a 4 inch deep pot with sand and peat as the substrate. It did well until moss start overtaking it. I pulled out the moss but it came back. Then it started growing out the drain holes. I tried keeping the water level up to the surface of the media but it still prefers growing out the drain holes. It has flowered for me several times, out the drain holes. I even took a cutting from the drain holes and repotted it on the surface - no go.
I gave a cutting away and the grower says it prefers to grow as an aquatic with 22 inches of water underneath being optimal.