Butterworth-filter x-shift

I have a signal and want to bandpass-filter it:

def butter_bandpass_prep(lowcut, highcut, fs, order=5):
    """Butterworth bandpass auxilliary function."""
    nyq = 0.5 * fs # Minimal frequency (nyquist criterion)
    low = lowcut / nyq
    high = highcut / nyq
    b, a = butter(order, [low, high], btype='band')
    return b, a

def butter_bandpass(src, lowcut, highcut, fs, order=5):
    """Butterworth bandpass filter."""
    b, a = butter_bandpass_prep(lowcut, highcut, fs, order=order)
    dst = lfilter(b, a, src)
    return dst

However, my signal does not start at zero which seems to cause problems as the filtered signal is shifted in x-direction. How can I compensate for this? Or maybe the butterworth filter is not the filter of choice?!

You can use filtfilt, which will filter the signal twice, once forwards and once backwards. This will eliminate all phase shifts, but double the stopband attenuation:

dst = filtfilt(b, a, src)