Environment Information

• Package version(s): (6.207.0)
• Browser and OS versions: (tested in Edge/Chrome)

Please provide a reproduction of the bug in a codepen:

It can be reproduced in https://fabricweb.azurewebsites.net/oufr/
for v6 and v7
for v6:
choose version higher than (6.207.0) and select button, set Split Button by
Theme: fluent, Scheme: strong

for v7:
for the v7 support fluent theme, just the same step as v6.
for the v7 not support fluent theme, set Split Button by Theme: MDL2, Scheme: strong.

Actual behavior:

We can just see the button without text in disable mode

Expected behavior:

We can see button and text in disable mode.

Priorities and help requested:

Are you willing to submit a PR to fix? (Yes, No)

Requested priority: (Blocking, High, Normal, Low)

Products/sites affected: (if applicable) SPDF as the fluent flight is on.