Steps to Reproduce:

• open up a world
• start flying (in creative mode)
• run "/execute in minecraft:the_nether run tp @p ~ ~ ~" Note: I would recommend going above y=128 so you don't get stuck in blocks
• you are no longer flying

Expected Behavior: You should still be flying. Going through a portal normally if you are flying lets you stay flying when you enter the other dimension.

further testing note: when you relog, you start flying again

Command to copy to reproduce:

/execute in minecraft:the_nether run tp @p ~ ~ ~