Depending on zoom level, spaces in underlined texts trigger added line thickness, sometimes above, sometimes below the regular line.
This looks like a spurious underline character and therefore is of more than just cosmetic relevance
The problem seems to be limited to screen rendering, if saved as pdf, the underline is of constant thickness:
SMath Studio: SMath Studio Desktop 0.99.6611.22150, x64
OS: Microsoft Windows NT 6.1.7601 Service Pack 1 (Windows 7 Professional Service Pack 1, x64)
Screen: 1920x1080 px, 96x96 dpi, 96 GP.DPI, 1 GP.SRF
Localization: separator=<semicolon>; decimal symbol=<comma>; system decimal symbol=<comma>; language=ENG
Frameworks: CLR 4.0.30319.42000
installed versions:
v2.0.50727 2.0.50727.5420 SP2
v3.0 3.0.30729.5420 SP2
v3.5 3.5.30729.5420 SP1
v4
Client 4.7.02053
Full 4.7.02053
v4.0
Client 4.0.0.0