Sounds like you're referring to the University of Baltimore/MICA light rail stop[0], where you have to get off if heading south or heading north but not on the Penn line, to catch the 'Penn Station - Camden Yards' line. I mean, it's in the name of the light rail line...it lets you off right at the station[1].
The real criticism of the light rail is that there's really _only_ one line, north to south. And the (part subway) metro train serves a similar route, NW to east side of downtown.[0]
99% of all the light rail "lines" ride the same track. The Penn-Camden "line" veers off the main tracks right at that Mt Royal stop (MICA/UB), and only goes to Penn, then back to the main line at Mt Royal, then headed to Camden Yards. It's probably the least common "line" to see.
