Expressions don't work for E motor values

Think I found a bug/limitation in the expression code. Verified using the latest beta (3.2beta3.2).
This expression is accepted, but doesn't update the E value:
M906 E{0.7*sqrt(2)*1400}
This one works:
M906 Z{0.7*sqrt(2)*1680}
Tested with expression for both my E with the same result.
M906 E{0.7*sqrt(2)*1400}:{0.7*sqrt(2)*1400}
Is this a known limitation?